Officials are investigating a possible arson at Huntington Beach High School.
Huntington Beach firefighters responded to a minor fire at 9:55 a.m. June 9 after a smoke detector in the boy's bathroom went off. School staff found the bathroom filled with smoke, said Deputy Fire Marshal Jeff Lopez.
The staff had already put out the blaze by the time firefighters arrived three minutes after the call, Lopez said.
Combustible materials were ignited and placed in the plumbing access door in the bathroom wall, Lopez said.
"We're assuming that it was done by a student," he said. "We expect it was done by a student versus a staff member. We'd be pretty surprised if it was done by a staff member."
Before leaving, the fire crew confirmed that it hadn't spread through the wall.
Huntington Beach police are assisting with the investigation.